1. Technical Field
The present invention relates to an ink composition that can provide a beautiful recorded material with stable discharge in higher-speed printing environments, to an ink set using an ink composition with these properties as one component, to an inkjet recording method using this ink set, and to a beautifully recorded material obtained by this recording method.
2. Related Art
Inkjet recording is a printing method whereby printing is accomplished by discharging droplets of ink from a fine nozzle head so that they fly through the air and adhere to a paper or other recording medium. The advantage of this method is that it allows high-resolution, high-quality images to be printed at high speeds using relatively simple equipment. Inkjet recording units using this method are widely used in the industry because they provide good printing quality at a low cost with relatively quiet operation and graphic formation ability. In particular, thermal (Bubble Jet®) and piezoelectric drop-on-demand printers have had great commercial success, and are widely used as computer printers in offices and homes.
The inks used in inkjet recording may be obtained for example by dissolving a dye as the coloring material in an aqueous solvent, but inks have also been proposed that are obtained by dispersing a pigment with a surfactant or polymer dispersant in an aqueous solution. A recent practice is to form color images by inkjet recording using ink sets consisting of multiple ink compositions. In general, color images are formed with 3 colors—a yellow ink composition, a magenta ink composition and a cyan ink composition—or in some cases with 4 colors including a black ink composition in addition to these. There are also cases in which color images are formed with 6 colors, including a light cyan ink composition and a light magenta ink composition in addition to the other 4, or with 7 colors, including a dark yellow ink composition in addition to the other 6. In multicolor printing using multiple color ink compositions consisting of different coloring materials, multiple coloring materials are mixed on the recording medium, providing uniform color development to create beautiful printed materials without color irregularities.
In recent years, “photographic quality” printing using color inkjet printers has reached a level equivalent to that of “silver salt photography” thanks to continuous improvements in heads, ink compositions, recording methods and media. In particular, by reducing the volume of the discharged ink droplets it has been possible to reduce graininess, which is indispensable for achieving photographic quality. Various proposals have also been made from time to time for increasing printing speed, as well as for improving head responsiveness and grading the weight of the ink droplets (JP-A-2006-255933, JP-A-2006-312331).
However, such increases in printing speed have also increased ink flow rates, leading to more contamination or generation of bubbles in the head channel. This interferes with normal discharge, leading to dot skipping in the image on the recording paper, and detracting from the image quality, so such bubbles need to be eliminated from the channel.